# motion and forces

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- Created by: ikayleigh
- Created on: 05-06-16 15:27

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- motion and forces
- stopping distance increase -increasing speed - a greater mass -reduced friction - increased reaction time
- air resistance (in gases) and drag (in liquids), from frictional forces between the fluid and an object, increase as -the objects speed increases -the fluid gets denser
- an object falling through a fluid, accelerates until it reaches terminal velocity, when the resultant force is zero :upthrust (fluid resistance force) = objects weight due to gravity
- every moving object has kinetic energy that can be transformed into other forms. An objects kinetic energy increases when its: - mass increases -speed increases
- using force to do work on an object gives energy work done=energy transferred
- the amount of work done depends on the force and the distance work done (J) = force (N) x distance moved in the direction of the force (m)
- every moving object has momentum that depends ion its mass and velocity momentum (kg m/s) =mass (kg) x velocity (m/s)
- momentum has size and direction and is conserved in collision and explosions
- forces changes and objects momentum by changing its velocity or direction. the bigger the force on a moving object, the larger its rate of changing momentum
- distance-time graphs helps us to "picture" how an object moves: -the slope on the graph shows the speed
- average speed=total distance travelled/total time travelled
- the velocity of an object tells us its speed in a given direction. acceleration is the rate of change of velocity. acceleration (m/s squared ) =change in velocity (m/s) /time taken to change (s)
- velocity-time graphs show how the velocity changes: -the slope shows the acceleration -the area under the graph shows the distance travelled
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- force can add up or cancel out to give a resultant force. When the resultant force is not zero, an object accelerates. the acceleration is: -directly proportional to force, a&f -inversely proportional to mass, a&1/m resultant force (bn) =mass (KG) x acceleration (M/s squared) F=ma
- for every force there is an equal and opposite force, balanced forces have the same value but act in opposite directions, e.g. a person floating in water has a balanced force
- objects moving at constant velocity (including terminal velocity) have balanced forces.
- stopping distance=thinking distance breaking distance thinking distance=speed x reaction time

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